The fabled Facebook phone is once again flitting to and fro, this time under the guise of the “Opera UL.” Well, maybe. We’ve seen this movie before – an unidentified phone shows up somewhere (this time it was in a benchmarking test), someone decides it’s simply got to be the Facebook phone, and the technorati go crazy. If I needed to set my wristwatch once a year, this rumor would be my reference point.

Though the details of the Facebook phone change, one thing has remained relatively constant: HTC. The smartphone maker, which previously partnered with T-Mobile, Google, and Verizon to create co- or re-branded phones, is often rumored to be Facebook’s hardware pal.

Surprised? Don’t be. With most everyone fixated on Apple – and, to a lesser degree, Samsung – HTC doesn’t get the respect it deserves. After all, the company popularized 4-inch smartphone screens, was the first to launch a phone on Sprint’s WiMax “4G” network, and shipped the first phone with support for Verizon’s LTE network. This expertise, combined with the fact that company profits tumbled 79 percent for the third quarter, helps make HTC Facebook’s ideal mystery date.

And, lest you forget, HTC has done its share of innovating. The first Android device was the HTC-built T-Mobile G1, which shipped in 2008. Clunky by today’s standards, the G1 looked like a mishmash of what phones were meant to look like pre- and post-iPhone. It had a touch screen, like the iPhone, but it also shipped with a full keyboard and a group of physical buttons underneath the screen. It wasn’t much, but it was a start. Since then HTC has built several of T-Mobile’s “myTouch” devices, numerous phones in the Verizon-branded “Droid” line, and the Nexus One phone with Google. Some of these devices – the Nexus phone, the original Droid Incredible – were, well, pretty incredible, and HTC was the king of Android’s metaphorical hill.

This continued with the Evo, the first smartphone to support Sprint’s “4G” WiMax network and the phone that kicked off the trend of ever-larger screens. While Apple and other manufacturers were still shipping phones with 3.5” or 3.7” screens, HTC went ahead and released a pocket-busting 4.3” behemoth. Then, as if that weren’t enough, the company’s Thunderbolt phone was the first to ship with support of Verizon’s LTE network (“true 4G”). When new tech came out, HTC was the one building a phone to take advantage.

Unfortunately, focus has never been HTC’s strong suit. The phones listed are only a portion of HTC’s products, cherry-picked from a vast product library. The company hasn’t just shipped the Evo – it’s also shipped the Evo 3D, the Evo 4G LTE, the Evo Design 4G, the Evo Shift 4G, the Flyer/Evo View 4G, and the Evo 4G+. That’s on top of the other phones, like the Droid Incredible and its Incredible 2 or Incredible S followups, its “One” line, and the ChaCha, a phone that shipped with a one-button link to Facebook. Apple produces a very limited line of products. HTC throws everything against the wall to see what sticks.

Now there’s the long-rumored Facebook phone. Naturally, Facebook denies it’s making one, and there’s no confirmation that this “Opera UL” is anything more than another Evo or Droid device in disguise (though another one of those leaked today as well). But don’t be surprised by a Facebook-HTC partnership. The company built the previously-mentioned ChaCha (typing that twice in one story genuinely hurts), which sported deep Facebook integration, and HTC has always been eager to partner with other companies for its devices. Many of these devices  are either exclusive to one carrier (the Thunderbolt, the Evo, and the Droid devices) or were built specifically for another company (the Nexus phone, the myTouch models). Plus, the Facebook phone would certainly be a huge “get” for any manufacturer.

But uh, oh. There’s still HTC’s pesky revenue problem. Because Apple is profiting from the iPhone and Samsung is, in turn, making out by copying/mimicking/whatever-ing Apple’s designs, HTC is left picking for scraps. Between this squeeze on the company’s finances and HTC’s history as a sort-of white label smartphone manufacturer, a deal with Facebook makes even more sense.

Of all of the smartphone makers (of which there are many) out there, HTC is the one with the most experience building phones for other companies, especially once Samsung, which seems to be happy building its own devices and Google’s Nexus products, and Nokia, which has a deal with Microsoft, are taken out of the picture.

So, if we see a Facebook phone, HTC’s name may be emblazoned on the back. Now that could be the beginning of a beautiful friendship.